1. Field of the Invention
This application relates to wrenching tools and, specifically, to torque-angle measuring and recording wrenches.
2. Description of the Prior Art
The object of a wrenching tool is to rotate or hold against rotation an item, such as a threaded fastener (e.g. a bolt) joining two objects together. As the fastener is tightened it is stretched until it exerts the appropriate amount of compression force (called “bolt load”) to the objects being held together or in place by the bolt. There is a relationship between the amount of torque that is applied to the head of a fastener and the amount of load applied to the joined objects. However, torque measurement is a poor method of determining ‘bolt load,’ because variations in frictional components vary the ‘bolt load’ achieved for a given torque applied.
Torque is considerably influenced by friction forces, the condition of the head, the amount, if any, of lubrication, as well as by other factors. The reliability of a torque measurement as an indication of desired load is, therefore, significantly variable. The solution is to rotate the bolt a specified number of degrees. This removes the friction-based error factor. Accordingly, a torque-angle fastener installation process, rather than torque measurement alone, is recommended in situations where tightening to recommended specifications is critical.
In a torque-angle fastener installation, a fastener is first tightened to a desired torque using a torque wrench; then the fastener is rotated through a predetermined additional angle of rotation. Because angle-based torquing is a more accurate way to ensure even tightening, more and more manufacturers are using the torque-angle procedure for tightening fasteners.
Another advantage of torque-angle installation is that like fasteners exert the same clamp forces without deviation from one fastener to the next due to variable conditions of lubrication, surface finish and the like previously mentioned.
At present, there are various wrenching tools available which meter angular rotation. Early angle measurement wrenching tools relied on some type of mechanical reference, usually a flexible strap connected to a “ground” clamp, for measurement of the angular rotation of a fastener.
More modern tools now use gyroscopes to meter angular rotation. One such device is disclosed in U.S. Pat. No. 4,262,528 to Holting et al. A gyroscope operates by offering opposition to a swiveling motion around an axis located transversely to its axis of rotation. Other torque-angle measuring tools on the market include KD Tools #3336 Torque Angle Gauge, Lisle Corp. #28100 Torque Angle Meter, SPX Corp. #4554 Stinger Torque Angle Gauge, Fel-Pro TRQ-1 Torque-to-Angle Indicator, and Kent-Moore J36660A Torque/Angle Meter. The disadvantages of these devices is that they require mechanical reference to a stationary point. This requires repositioning the reference arm for every fastener to be tightened, and a poorly positioned arm could cause gross errors in measurement, perhaps leading to component failure.
Still other similar devices come at a very high price (>US$1,200) and include complex menu-driven operation, which in some markets, such as automotive, may be prohibitive.
The present instrument in its various embodiments provides a solution to these and other problems in the relevant field.